package main

import (
	"errors"
	"fmt"
	"math"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"syscall"
	"time"
)

// unit is the name picom runs under in the account's service manager when a tool starts it. The
// session start runs its own, and a tool that starts one first ends any other (Toggle, Restart).
const unit = "picom"

func configPath() string { return filepath.Join(operatorHome(), ".config", "picom", "picom.conf") }

// Running is picom's processes of this account.
func running() []int { return processesOf("picom") }

// RestartResult is what picom_restart answers.
type RestartResult struct {
	Action string `json:"action"`
	PIDs   []int  `json:"pids"`
	Note   string `json:"note,omitempty"`
}

// Restart tells a running picom to reinitialise, or starts one.
func Restart(hard bool) (RestartResult, error) {
	if pids := running(); len(pids) > 0 && !hard {
		return RestartResult{Action: "reinitialised", PIDs: signalAll("picom", syscall.SIGUSR1),
			Note: "picom re-read " + configPath()}, nil
	}
	s, err := findSession()
	if err != nil {
		return RestartResult{}, err
	}
	if err := stopAll(); err != nil {
		return RestartResult{}, err
	}
	if err := s.detach(unit, "picom", "--config", configPath()); err != nil {
		return RestartResult{}, err
	}
	pids := waitFor(func() []int { return running() }, 3*time.Second)
	return RestartResult{Action: "started", PIDs: pids,
		Note: "started under the account's service manager as " + unit + ".service"}, nil
}

// stopAll ends every picom of this account and waits for them to go.
func stopAll() error {
	signalAll("picom", syscall.SIGTERM)
	deadline := time.Now().Add(3 * time.Second)
	for time.Now().Before(deadline) {
		if len(running()) == 0 {
			return nil
		}
		time.Sleep(100 * time.Millisecond)
	}
	if left := running(); len(left) > 0 {
		return fmt.Errorf("picom %v did not end within 3s", left)
	}
	return nil
}

func waitFor(get func() []int, within time.Duration) []int {
	deadline := time.Now().Add(within)
	for {
		if got := get(); len(got) > 0 || time.Now().After(deadline) {
			return got
		}
		time.Sleep(100 * time.Millisecond)
	}
}

// ToggleResult is what picom_toggle answers.
type ToggleResult struct {
	Compositing bool   `json:"compositing"`
	PIDs        []int  `json:"pids"`
	Note        string `json:"note"`
}

// Toggle stops or starts compositing; want nil flips it.
func Toggle(want *bool) (ToggleResult, error) {
	on := len(running()) == 0
	if want != nil {
		on = *want
	}
	if !on {
		if err := stopAll(); err != nil {
			return ToggleResult{}, err
		}
		return ToggleResult{Compositing: false, PIDs: []int{},
			Note: "picom ended; the session start runs it again at the next login, or call picom_toggle with on"}, nil
	}
	if pids := running(); len(pids) > 0 {
		return ToggleResult{Compositing: true, PIDs: pids, Note: "picom was already running"}, nil
	}
	r, err := Restart(true)
	if err != nil {
		return ToggleResult{}, err
	}
	return ToggleResult{Compositing: len(r.PIDs) > 0, PIDs: r.PIDs, Note: r.Note}, nil
}

// Rule is one window rule, its options as written.
type Rule struct {
	Match   string            `json:"match"`
	Options map[string]string `json:"options"`
}

// RulesResult is what picom_rules answers.
type RulesResult struct {
	File    string            `json:"file"`
	Running []int             `json:"running"`
	Global  map[string]string `json:"global"`
	Rules   []Rule            `json:"rules"`
	// Legacy names options that window rules supersede, which picom ignores when rules are set.
	Legacy []string `json:"legacy,omitempty"`
}

var (
	commentLine = regexp.MustCompile(`(?m)^\s*#.*$`)
	rulesBlock  = regexp.MustCompile(`(?s)\brules\s*[=:]\s*\((.*?)\)\s*;`)
	ruleGroup   = regexp.MustCompile(`(?s)\{(.*?)\}`)
	assignment  = regexp.MustCompile(`(?m)^\s*([A-Za-z][A-Za-z0-9-]*)\s*[=:]\s*(.+?)\s*;?\s*$`)
)

// superseded are the options picom's window rules replace (picom(1), WINDOW RULES).
var superseded = []string{"opacity-rule", "inactive-opacity", "active-opacity", "inactive-dim",
	"shadow-exclude", "fade-exclude", "focus-exclude", "rounded-corners-exclude", "blur-background-exclude",
	"corner-radius-rules", "wintypes", "inactive-opacity-override", "mark-wmwin-focused"}

// Rules reads picom's configuration file into its global options and its window rules.
func Rules(path string) (RulesResult, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return RulesResult{}, fmt.Errorf("picom's configuration: %w", err)
	}
	return parseRules(path, string(raw), running()), nil
}

func parseRules(path, conf string, pids []int) RulesResult {
	out := RulesResult{File: path, Running: pids, Global: map[string]string{}, Rules: []Rule{}}
	conf = commentLine.ReplaceAllString(conf, "")
	rest := conf
	if m := rulesBlock.FindStringSubmatchIndex(conf); m != nil {
		body := conf[m[2]:m[3]]
		rest = conf[:m[0]] + conf[m[1]:]
		for _, g := range ruleGroup.FindAllStringSubmatch(body, -1) {
			r := Rule{Options: map[string]string{}}
			for _, part := range strings.Split(g[1], ";") {
				k, v, ok := strings.Cut(part, "=")
				if !ok {
					continue
				}
				k, v = strings.TrimSpace(k), strings.TrimSpace(v)
				if k == "match" {
					r.Match = unquote(v)
				} else {
					r.Options[k] = unquote(v)
				}
			}
			out.Rules = append(out.Rules, r)
		}
	}
	for _, m := range assignment.FindAllStringSubmatch(rest, -1) {
		out.Global[m[1]] = unquote(strings.TrimSuffix(m[2], ";"))
	}
	if len(out.Rules) > 0 {
		for _, name := range superseded {
			if _, set := out.Global[name]; set {
				out.Legacy = append(out.Legacy, name)
			}
		}
	}
	return out
}

func unquote(v string) string {
	v = strings.TrimSpace(v)
	if len(v) >= 2 && v[0] == '"' && v[len(v)-1] == '"' {
		return v[1 : len(v)-1]
	}
	return v
}

// OpacityResult is what picom_window_opacity answers.
type OpacityResult struct {
	Window string `json:"window"`
	Class  string `json:"class,omitempty"`
	Title  string `json:"title,omitempty"`
	// Opacity is the window's own value in percent; nil when it has none.
	Opacity *int   `json:"opacity"`
	Note    string `json:"note,omitempty"`
}

var (
	activeWindow = regexp.MustCompile(`window id # (0x[0-9a-fA-F]+)`)
	cardinal     = regexp.MustCompile(`_NET_WM_WINDOW_OPACITY\(CARDINAL\) = (\d+)`)
	wmClass      = regexp.MustCompile(`WM_CLASS\(STRING\) = "[^"]*", "([^"]*)"`)
	wmName       = regexp.MustCompile(`_NET_WM_NAME\(UTF8_STRING\) = "(.*)"`)
)

// WindowOpacity reads a window's own opacity, and sets it when percent is 0-100.
func WindowOpacity(window string, percent int) (OpacityResult, error) {
	s, err := findSession()
	if err != nil {
		return OpacityResult{}, err
	}
	if window == "" {
		r, err := s.run(5*time.Second, "", "xprop", "-root", "_NET_ACTIVE_WINDOW")
		if err != nil {
			return OpacityResult{}, err
		}
		m := activeWindow.FindStringSubmatch(r.Stdout)
		if m == nil || m[1] == "0x0" {
			return OpacityResult{}, errors.New("no window is focused")
		}
		window = m[1]
	}
	id, err := windowID(window)
	if err != nil {
		return OpacityResult{}, err
	}
	if percent >= 0 {
		var r Result
		if percent == 100 {
			r, err = s.run(5*time.Second, "", "xprop", "-id", id, "-remove", "_NET_WM_WINDOW_OPACITY")
		} else {
			r, err = s.run(5*time.Second, "", "xprop", "-id", id, "-f", "_NET_WM_WINDOW_OPACITY", "32c",
				"-set", "_NET_WM_WINDOW_OPACITY", strconv.FormatUint(opacityCardinal(percent), 10))
		}
		if err != nil {
			return OpacityResult{}, err
		}
		if r.Code != 0 {
			return OpacityResult{}, fmt.Errorf("xprop: %s", strings.TrimSpace(r.Stderr))
		}
	}
	r, err := s.run(5*time.Second, "", "xprop", "-id", id, "_NET_WM_WINDOW_OPACITY", "WM_CLASS", "_NET_WM_NAME")
	if err != nil {
		return OpacityResult{}, err
	}
	if r.Code != 0 {
		return OpacityResult{}, fmt.Errorf("window %s: %s", id, strings.TrimSpace(r.Stderr))
	}
	out := parseWindow(id, r.Stdout)
	if rules, err := Rules(configPath()); err == nil && out.Class != "" {
		for _, rule := range rules.Rules {
			if _, sets := rule.Options["opacity"]; sets && strings.Contains(rule.Match, "class_g = '"+out.Class+"'") {
				out.Note = "a window rule sets the opacity of class " + out.Class + " and outranks the window's own value"
			}
		}
	}
	return out, nil
}

func windowID(w string) (string, error) {
	w = strings.TrimSpace(strings.ToLower(w))
	base := 10
	if strings.HasPrefix(w, "0x") {
		w, base = w[2:], 16
	}
	n, err := strconv.ParseUint(w, base, 32)
	if err != nil || n == 0 {
		return "", fmt.Errorf("window %q is not an X window id", w)
	}
	return fmt.Sprintf("0x%x", n), nil
}

func opacityCardinal(percent int) uint64 {
	return uint64(math.Round(float64(percent) / 100 * float64(math.MaxUint32)))
}

func parseWindow(id, out string) OpacityResult {
	r := OpacityResult{Window: id}
	if m := cardinal.FindStringSubmatch(out); m != nil {
		n, _ := strconv.ParseUint(m[1], 10, 64)
		p := int(math.Round(float64(n) / float64(math.MaxUint32) * 100))
		r.Opacity = &p
	}
	if m := wmClass.FindStringSubmatch(out); m != nil {
		r.Class = m[1]
	}
	if m := wmName.FindStringSubmatch(out); m != nil {
		r.Title = m[1]
	}
	return r
}